The present invention relates to a retractable undercarriage for an aircraft, and more particularly, pertains to an undercarriage for the fuselage of an aircraft wherein the sets of landing gear are pivotably connected to the fuselage of the aircraft, and are designed to recede into this fuselage upon retraction.
Fuselage undercarriages are often utilized in situations wherein it is not practical to fasten the undercarriages beneath the wings of an aircraft, either because the latter are too high or too thick, or because the wings have a variable geometry. The retractable wheels of a fuselage undercarriage occupy a minimal space when the axes about which they pivot are placed perpendicular to the plane of symmetry of the aircraft, but in an arrangement of this type when the undercarriages are placed in a "landing gear down-locked" position the distance between the wheels of the undercarriages is too small to provide sufficient stability for the aircraft.
This disadvantage has been compensated for by selectively tilting the axes about which the undercarriages pivot relative to the plane of symmetry of the aircraft. However, in an arrangement of this nature when the landing gear is in the down-locked position, an angular relationship exists between the oblique strut of the undercarriage and the wheels, which are perpendicular to the ground. When the undercarriage is retracted, the angular relationship results in the wheels being positioned obliquely in the fuselage which has the effect of increasing the required volume of the landing gear well.
It is well recognized in the fuselage undercarriage art that when the wheels are in a flat position in the "undercarriage retracted" mode they occupy a minimal volume of the undercarriage housing. In fuselage undercarriages of this type, each strut of the undercarriage is integral with the structure of the aircraft fuselage and is pivoted about an axis of retraction which is positioned obliquely relative to the longitudinal plane of symmetry of the aircraft. In this arrangement either the strut or the wheels are supported by an element capable of pivoting in relation to the undercarriage, either in a first approach around the axis of the strut or a part thereof, or in a second approach around a substantially longitudinal axis. In both approaches the wheel supporting element is pivoted by a complex mechanism connected to the strut and/or the wheel bearing element and/or the structure of the aircraft which assures a locked relationship of the strut to the wheel supporting element in its load bearing position. Alternatively, hydraulic actuating cylinders which accomplish the same functions as the complex mechanism are added to the operating jack. These approaches have disadvantages, the first on the basis of weight, because it requires a complex, structurally strong and therefore heavy motor assemblage, and the second on the basis of cost, because it requires an additional hydraulic actuating cylinder.